1. Field of the Invention
The present invention relates to surgical instrumentation, and more particularly surgical drill handpieces. More specifically, the invention relates to handpieces for driving otology burs and guards therefor which are advantageously used during a cochleostomy and other surgical procedures in which it is desired to protect one anatomic structure by controlling the depth of a cutting instrument while removing another structure with the cutting instrument.
2. State of the Art
A cochlear implant is a hearing device that can be implanted in an individual with a severe or profound sensorineural hearing loss to directly stimulate the cochlear nerves and restore hearing. When successfully implanted, the cochlear implant restores a sufficient sense of sound, albeit with a different quality than natural sound, so that the recipient is able to hear and understand speech and environmental sounds. The performance of the cochlear implant is greater when there is some residual acoustic hearing capacity and a hearing aid is used in conjunction with the cochlear implant. See, for example, U.S. Pat. No. 8,126,564 to Gantz. In order to preserve the acoustic hearing, it is of vital importance that the membranous structures of the cochlea not be damaged during the surgical implant procedure.
The implant includes an external portion and an internal portion. The external portion is surgically placed under the skin behind the ear, and includes one or more microphones which picks up sound from the environment, a speech processor which selectively filters sound to prioritize audible speech, splits the sound into channels and sends the electrical sound signals through a thin cable to the transmitter, and a transmitter, which is a coil held in position by a magnet placed behind the external ear, and transmits power and the processed sound signals across the skin to the internal device by electromagnetic induction. The internal portion is secured in the cochlear bone beneath the skin, and includes a receiver and stimulator, which converts the signals into electric impulses and sends them through an internal cable to electrodes. The electrodes are wound through the cochlea, send the impulses to the nerves in the scala tympani and then directly to the brain through the auditory nerve system.
In order to pass the electrodes, a small hole must be drilled into the bony cochlea. A high-speed bur driving surgical handpiece is used to drill into the cochlea. However, it is a very delicate procedure, and extreme precision is required to ensure that the hole is drilled through the boney outer surface of the cochlea, but that no damage results to the interior cochlear membranes. The difficulty is rendered higher given that the depth of the boney surface is not consistent among patients. The surgeon must progressively remove bone from the cochlear wall while visually observing the color change at the bony surface to determine when the cochlear wall is about to be penetrated with the bur.
In such procedures, it is known to use a bur guard about the rotating shaft of the bur to protect peripherally surrounding tissue from the rapidly rotating shaft of the bur. However, such burs do not practically operate to limit the drilling depth of the bur.